msm: camera: mem_mgr: Add refcount to track in use buffers

The function cam_mem_mgr_release can unmap the buffers when in use.

This change prevents unmapping the buffers when in use.

CRs-Fixed: 3489559
Change-Id: I2e72e795d39ac15abfa56c19043c419a03686966
Signed-off-by: Shivakumar Malke <quic_smalke@quicinc.com>
Signed-off-by: Gaurav Jindal <quic_gjindal@quicinc.com>